BBC Micro, factory B with Econet has had a disc interface fitted at some point. All the Econet ICs had been removed except IC91 as it is shared with the disc interface. I replaced the Econet ICs and I could see the banner for Econet that reported the correct station ID and the presence of a clock. However, booting from the network made the machine hang.
Putting the scope on, I checked the NMI for Econet and it was not present, I went back to the ADLC/68B54/IC89 pin #7 and it was dropping low on RESET as I would expect.
Then I moved to check the Schmitt NAND/74LS132/IC91 pin#13 and the signal was present, I then checked pin #12 and that was at +5V as it should be, then I checked pin #11 and this should have been wiggling up and down, but it was stuck at 0V.
I was thinking about replacing IC91, but it's not in a socket. So I removed the board to take out IC91 as I assumed it was dead.
Ah-ha! no, it's not the IC! someone had made a bridge across S2 on the underside of the board with a blob of solder. D'oh! I removed the blob and all is good now.
TLDR: check S2 is not short with a multimeter before installing Econet...
Putting the scope on, I checked the NMI for Econet and it was not present, I went back to the ADLC/68B54/IC89 pin #7 and it was dropping low on RESET as I would expect.
Then I moved to check the Schmitt NAND/74LS132/IC91 pin#13 and the signal was present, I then checked pin #12 and that was at +5V as it should be, then I checked pin #11 and this should have been wiggling up and down, but it was stuck at 0V.
I was thinking about replacing IC91, but it's not in a socket. So I removed the board to take out IC91 as I assumed it was dead.
Ah-ha! no, it's not the IC! someone had made a bridge across S2 on the underside of the board with a blob of solder. D'oh! I removed the blob and all is good now.
TLDR: check S2 is not short with a multimeter before installing Econet...
Statistics: Posted by maniacminer — Sun Feb 09, 2025 12:23 am
